Then Allah says,

فَأَيْنَ تَذْهَبُونَ ﴿٢٦﴾

Then where are you going,

meaning, where has your reason gone, in rejecting this Qur'an, while it is manifest, clear, and evident that it is the truth from Allah.

This is as Abu Bakr As-Siddiq said to the delegation of Bani Hanifah when they came to him as Muslims and he commanded them to recite (something from the Qur'an). So they recited something to him from the so called Qur'an of Musaylimah the Liar, that was total gibberish and terribly poor in style.

Thus, Abu Bakr said,

"Woe unto you! Where have your senses gone By Allah, this speech did not come from a god.''

Qatadah said, فَأَيْنَ تَذْهَبُونَ (Then where are you going) meaning, from the Book of Allah and His obedience.